KR100395100B1 - Manufacturing method of non-oriented electrical steel sheet with excellent magnetic properties after heat treatment - Google Patents

Abstract

The present invention relates to a method for manufacturing non-oriented electrical steel sheet used as iron cores of electrical equipment such as various motors and transformers; The purpose is to provide a method for producing non-oriented electrical steel sheet having excellent magnetic properties after heat treatment.

The present invention for achieving the above object, in weight%, C: 0.02% or less, Si: 1.5% or less, Mn: 1.5% or less, P: 0.15% or less, S: 0.02% or less, Sol.Al: 0.005% N: 0.007% or less, Sn: 0.03-0.3%, Ni: 0.05-0.6%, Cu: 0.05-0.5%, or the above Sol.Al is 0.05% or less, B: 0.0005-0.0050% and the rest The slab composed of Fe and other inevitably contained impurities is reheated to 1100-1300 ° C., hot rolled, wound up to a temperature of 800 ° C. or lower, then pickled, followed by cold rolling at a reduction rate of 70% or more, and then 5 ° C. Magnetic demand after heat treatment, including heating at a rate of more than / sec, annealing for 30 seconds-5 minutes in the temperature range of 600-800 ℃, and then stress relief annealing in the temperature range of 700-850 ℃ after processing demand The technical gist of this excellent non-oriented electrical steel sheet is described.

Description

Manufacturing method of non-oriented electrical steel sheet having excellent magnetic properties after heat treatment

The present invention relates to a method for manufacturing non-oriented electrical steel sheet used as iron cores of electric machines such as various motors and transformers, and more particularly, to a method for manufacturing non-oriented electrical steel sheet having excellent magnetic properties after heat treatment.

Non-oriented electrical steel sheets used for iron loss in electric equipment such as motors and transformers are required to have low magnetic loss and high magnetic flux density among magnetic properties. Iron loss is expressed in watts per kilogram (weight) of non-oriented electrical steel sheet, which is expressed as w / kg, which means energy loss. Magnetic flux density refers to the extent to which magnetic flux is generated in any magnetic field, and indicates the strength and efficiency of an electric device. Generally, materials having high magnetic flux density and permeability but low iron loss are preferable.

On the other hand, non-oriented electrical steel sheet is manufactured by dividing the semi-process material and pulley process material. Semi-process materials are products that are cold rolled after annealing the cold rolled sheet and shipped at demand, and pulley process materials are products that are shipped at the demand price after annealing the cold rolled sheet. Such a semi-process product has a disadvantage in that light rolling must be additionally performed during manufacturing of the product.

Korean Patent Application No. 18626 (1991.10.22) provides a method for producing a pulley process for annealing a hot rolled sheet and a method for producing a semi-process for performing light rolling of 2-15%. These manufacturing methods have the disadvantage of annealing the hot rolled plate, and also has the disadvantage of securing the characteristics of the semi-processed product should be subjected to light rolling.

An object of the present invention is to provide a non-oriented electrical steel sheet having a high magnetic flux density and high permeability while having low iron loss after heat treatment even without hot rolling annealing and light rolling.

The production method of the present invention for achieving the above object, in weight%, C: 0.02% or less, Si: 1.5% or less, Mn: 1.5% or less, P: 0.15% or less, S: 0.02% or less, Sol.Al : Slab composed of less than 0.005%, less than N: 0.007%, less than Sn: 0.03-0.3%, less than Ni: 0.05-0.7%, less than Cu: 0.03-0.5%, remaining Fe and other unavoidable impurities. Reheated, hot rolled, wound up to a temperature below 800 ° C, pickled, cold rolled to 70% or more, and then heated at a rate of 5 ° C / sec or more for 30 seconds at a temperature range of 600-800 ° C. Annealing for -5 minutes, followed by stress relief annealing in the temperature range of 700-850 ° C after demand processing.

In addition, the manufacturing method of this invention is C: 0.02% or less, Si: 1.5% or less, Mn: 1.5% or less, P: 0.15% or less, S: 0.02% or less, Sol.Al: 0.05% or less by weight% Slabs composed of N: 0.007% or less, Sn: 0.03-0.3%, Ni: 0.05-0.7%, Cu: 0.03-0.5%, B: 0.0005-0.0050%, remaining Fe and other unavoidable impurities Reheat to -1300 ℃, hot rolled, wound up to temperature below 800 ℃, pickled, then cold rolled to 70% or more reduction rate, and then heated at a rate of 5 ℃ / sec or higher to 600-800 ℃ Annealing for 30 seconds to 5 minutes, followed by stress relief annealing in the temperature range of 700-850 ° C. after the demand processing.

Hereinafter, the present invention will be described in detail.

The present inventors have studied to produce a non-oriented electrical steel sheet having excellent magnetic properties after heat treatment without hot-rolled sheet annealing and light rolling, in order to achieve the object of the present invention, the cold-rolled sheet that has been conventionally strained Unlike high temperature annealing to remove residual stress to secure magnetism, the steel slab and its manufacturing conditions were selected appropriately by annealing at a relatively low temperature to find that the demand was heat-treated.

That is, the present invention is hot-rolled steel slab to which Sn, Ni, Cu or B is added to a conventional non-oriented electrical steel sheet, cold-rolled at a drop-down rate and then annealed at a relatively low temperature to maintain the residual stress in the state When stress relief annealing after processing, it is to improve the magnetism by the development of an advantageous texture for magnetism.

To this end, first of all, the steel slab C is the iron core of the electric equipment, which causes magnetic aging during use, which deteriorates the magnetic properties. Therefore, the slab should be 0.02% or less in the slab and 0.003% or less in the final product.

The Si is an element that increases the specific resistance and lowers the eddy current loss during iron loss, but in the present invention which performs the cold reduction rate of 70% or more, it is limited to 1.5% or less in consideration of rolling property.

The Mn is an element effective for improving the iron loss, but when added excessively, cold rolling may be difficult, so it is limited to 1.5% or less.

The P increases the specific resistance but may be added up to 0.15% in consideration of cold rolling.

The S is advantageously managed as low as possible by forming MnS, which is a fine precipitate, to suppress grain growth, and in the present invention, it is preferably contained at most 0.02% or less.

While Al plays a role of lowering eddy current loss by increasing specific resistance, it forms a fine precipitate of AlN and plays a role of suppressing grain growth, so it is not preferably added if possible, but is inevitably added for deoxidation during steelmaking. Considering the side to be taken, it should be less than 0.005%. In the present invention, when B is added, B is easily combined with nitrogen to form coarse precipitate, BN, thereby reducing the influence of N, thereby reducing the risk of AlN precipitate formation. Therefore, the Al content is added up to 0.05%. .

N is suppressed as much as possible by forming fine and long AlN precipitates, and in the present invention, it is added at 0.007% or less.

The Sn segregates at grain boundaries to suppress diffusion of N and to suppress the texture of the (222) plane which is disadvantageous to magnetism. It is necessary to add more than 0.03% for this role, but if more than 0.30% cold rolling is worse, in the present invention, the content of Sn is added as 0.03-0.30%.

Ni is an element that improves texture, and at least 0.05% has an effect thereof, but considering that Mn affecting cold rolling is added at most 1.5%, Ni content is less than 0.7% in terms of securing cold rolling property. Is added.

The Cu is an element that improves the corrosion resistance and develops the texture. For this purpose, more than 0.03% of Cu is added. However, when the content exceeds 0.5%, the plate shape of the hot rolled sheet is deteriorated. Therefore, the Cu content is preferably 0.03-0.5%. .

B is added by inhibiting formation of fine precipitates AlN and facilitating grain growth by forming coarse precipitates BN. If the amount is excessively high, more precipitates are added, and the amount of B is at least 0.0005-0.0050% because the amount is too small.

Hereinafter, the manufacturing conditions of the steel slab will be described.

The steel slabs formed as described above are made of slabs in a continuous casting process after being made of molten steel in steelmaking, and the steel slabs are charged into a heating furnace before hot rolling and heated to a temperature range of 1100-1300 ° C. . The reason is that hot rolling is easy when the slab reheating temperature is 1100 ° C. or higher, but when it exceeds 1300 ° C., precipitates harmful to magnetism, such as AlN and MnS, are re-dissolved and minute precipitates are excessively generated after hot rolling.

Reheating as described above and hot rolling in a conventional manner, the finish rolling temperature at this time is appropriately selected so that the oxide layer of the hot rolled sheet is not excessively generated, for example, the finish rolling temperature is 800-950 ℃ It is.

Winding of the hot rolled sheet obtained by hot rolling as mentioned above is performed at the temperature of 800 degrees C or less, and obtains the stable phase of a ferrite phase. The coiling temperature at this time is performed at a temperature of 800 ° C. or lower so that an oxide layer is not excessively generated on the hot rolled sheet. Cooling after winding can be cooled in a coil state in air, and more preferably furnace cooling.

The hot rolled sheet wound and wound as described above is cold rolled after pickling without performing hot rolled sheet annealing. Cold rolling is rolled to a rolling reduction rate of at least 70% to obtain a cold rolled sheet, followed by final annealing.

The final annealing at this time is preferably heated to a temperature range of 600-800 ℃ at a rate of 5 ℃ / sec or more and continuously annealing for 30 seconds-5 minutes. The reason for this is that when the heating rate is 5 ° C / sec or more, the (200) plane, which is an advantageous structure for magnetism, is generated in the material, and when such a material is stress-annealed, the (200) plane is grown into the generated material. Magnetism can be improved. In addition, if the final annealing temperature is lower than 600 ℃, there is a disadvantage that excessive rolling structure remains in the material, so that the demand is difficult to process during processing. If the final annealing temperature is higher than 800 ℃, the residual stress in the material is lost, so the demand is stressed. There is a disadvantage that the degree of improvement of the magnetic properties of the material during removal annealing is small.

The annealing plate continuously annealed as described above is shipped at the demand price after the insulation coating treatment. The insulating coating may be treated with organic, inorganic and organic / inorganic composite coatings, or may be coated with other insulating coatings.

The demanded product is stressed annealing in a non-oxidizing atmosphere for more than 30 minutes at a temperature of 700-850 ℃ after punching out, because stress stress annealing at temperatures below 700 ℃ may cause residual stress in the material This is because stress relief annealing at temperatures higher than 850 ° C. may damage the insulating film.

In the present invention, the hot rolled sheet is cold rolled, the heating rate of the cold rolled sheet is reduced during final annealing, and the annealing temperature is lowered. It can be improved.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Example 1

Steel slabs having the components shown in Table 1 below were prepared. The steel slabs were heated at a temperature of 1200 ° C., hot rolled to a finish rolling temperature condition of 860 ° C., and cooled in air after winding at a temperature of 720 ° C.

After the pickling, the hot rolled sheet was cold rolled and annealed as shown in Table 2 below. The final annealing atmosphere was atmosphere of 20% hydrogen and 80% nitrogen. After the annealing plate is coated with an organic-inorganic composite coating, the stress is annealed by non-oxidizing component crisis for 2 hours at the temperature of 750 ℃, and then the magnetic properties and (200) surface strength are investigated and the results are shown. 2 is shown. At this time, the surface strength is represented by the aggregate structure strength according to Horta equation.

Steel grade Chemical composition (% by weight) C Si Mn P S Al N Sn Ni Cu B Invention steel a 0.004 0.51 1.23 0.013 0.004 0.001 0.0021 0.12 0.24 0.15 - b 0.003 0.52 1.24 0.019 0.003 0.003 0.0025 0.08 0.22 0.30 - c 0.003 0.55 1.24 0.011 0.004 0.031 0.0032 0.13 0.15 0.31 0.0025 Comparative steel a 0.004 0.56 1.22 0.011 0.005 0.091 0.0027 0.12 0.25 0.17 - b 0.004 0.53 1.23 0.018 0.003 0.151 0.0030 0.12 0.16 0.30 0.0024

Sample Number Final Annealing Condition _Iron loss (W _15/50 ) W / kg Magnetic flux density (B ₅₀ ) Permeability (μ _1.5 ) (200) cotton strength Steel grade Annealing Temperature (℃) Heating rate (℃ / sec) Annealing time (minutes) Comparative Material 1 700 3 2 3.82 1.72 3100 0.22 Inventive Steel a Invention 1 700 6 2 3.57 1.77 4850 0.45 Inventive Steel a Invention 2 650 10 2 3.50 1.78 5200 0.51 Inventive Steel a Comparative Material 2 550 10 2 3.90 1.73 2830 0.25 Inventive Steel a Comparative Material 3 850 10 2 3.79 1.72 2760 0.31 Inventive Steel a Invention 3 650 15 One 3.62 1.76 4560 0.45 Inventive Steel b Invention 4 750 15 One 3.40 1.78 5120 0.57 Invention steel c Comparative Material 4 700 10 2 3.91 1.72 2500 0.31 Comparative Steel a Comparative Material 5 800 10 2 3.80 1.71 2430 0.27 Comparative Steel a Comparative Material 6 700 10 2 4.15 1.70 2250 0.24 Comparative Steel b _Iron loss (W _15/50 ): Loss magnetic flux density when magnetized to 1.5 Tesla at 50 Hz (B ₅₀ ): Magnetic flux density permeability induced when magnetized to 5000 A / m (μ _1.5 ): Magnetic field magnetic flux density of _1.5 Tesla Permeability when abandoning

As shown in Table 1 and Table 2, it was found that the inventive material (1-4) is superior in magnetic properties than the comparative material (1-6). In detail, the comparative material 1 had a low heating rate at the time of final annealing due to insufficient development of the aggregate structure of the (200) plane and low magnetic properties. The comparative material 2 had a low final annealing temperature, and the comparative material 3 had a low magnetization because the final annealing temperature was too high. In the case of the comparative materials (4) and (5), the conditions of the present invention were satisfied in the manufacturing conditions, but the Al content in the steel component was higher than the range of the present invention, resulting in low magnetic properties. In the case of the comparative material (6), the Al content was higher than the conditions of the present invention, which appeared to be the cause of the magnetic degradation.

Example 2

By weight C: 0.0025%, Si: 0.75%, Mn: 0.96%, P: 0.065%, S: 0.003%, Al: 0.0007%, N: 0.0007%, Sn: 0.12%, Ni: 0.25%, Cu: The slab, which is 0.25% and composed of the remaining Fe and other impurities, was heated to 1150 ° C., hot rolled to a thickness of 2.3 mm, wound up at a temperature of 800 ° C., and then cooled in a sealed annealing furnace. The furnace-cooled hot rolled sheet was cold rolled to a thickness of 0.5 mm after pickling. The cold rolled plate was heated at a rate of 15 ° C./sec and finally annealed at an annealing temperature of 700 ° C. for 2 minutes in an atmosphere of 20% hydrogen and 80% nitrogen. After the final annealing, the organic and inorganic mixed insulation coating was continuously applied and then cut. The primary magnetic properties were investigated and the results are shown in Table 3 below. Then, the specimen cut as described above was stress-annealed in an atmosphere of 100% nitrogen for 1.5 hours at a temperature of 750 ℃ and the secondary magnetic properties were investigated and the results are also shown in Table 3.

division _Iron loss (W _15/50 ) W / kg Magnetic flux density (B ₅₀ ) Permeability (μ _1.5 ) (200) cotton strength Crystal grain size (㎛) Primary magnetic properties (before stress relief annealing) 5.10 1.76 1990 - - Second magnetic property (after stress relief annealing) 3.35 1.77 4200 0.58 120

As shown in Table 3, the iron loss after the stress relief annealing was improved by 34% compared to the iron loss before the stress relief annealing.

Example 3

C: 0.003%, Si: 0.82%, Mn: 0.25%, P: 0.015%, S: 0.004%, Al: 0.015%, N: 0.0024%, Sn: 0.13%, Ni: 0.25%, Cu: Slab composed of 0.21% and B: 0.0015% and consisting of the remaining Fe and other impurities is heated under the conditions shown in Table 4 below, hot rolled to 2.1 mm thick, wound, pickled and cold rolled to 0.5 mm thick. It was. The cold rolled sheet was heated at a rate of 17 ° C./sec and annealed for 1 minute at a temperature of 680 ° C. in a dry atmosphere of 30% hydrogen and 70% nitrogen. After annealing as described above, the insulation film of the eumugi mixture was continuously coated and then cut, and the magnetic properties were investigated after stress relief annealing in a reducing atmosphere as shown in Table 3 and the results are shown in Table 3 below.

Sample Number Slab reheating temperature (℃) Hot Rolled Sheet Winding Temperature (℃ / sec) Stress Relieving Annealing Temperature (℃) _Iron loss (W _15/50 ) W / kg Magnetic flux density (B ₅₀ ) Permeability (μ _1.5 ) (200) cotton strength Steel grade Invention 5 1150 720 800 3.42 1.76 4240 0.43 Inventive Steel a Invention 6 1250 720 800 3.39 1.76 4510 0.49 Inventive Steel a Comparative Material7 1350 720 800 3.7 1.73 2650 0.27 Inventive Steel a Invention 7 1200 600 700 3.52 1.77 4530 0.49 Inventive Steel b Invention Material 8 1200 600 750 3.41 1.78 5050 0.61 Invention steel c _Iron loss (W _15/50 ): Loss magnetic flux density when magnetized to 1.5 Tesla at 50 Hz (B ₅₀ ): Magnetic flux density permeability induced when magnetized to 5000 A / m (μ _1.5 ): Magnetic field magnetic flux density of _1.5 Tesla Permeability when abandoning

As shown in Table 4, the comparative material (7), but the steel component satisfies the conditions of the present invention, the slab reheating temperature is excessively high so that finely precipitated MnS is re-dissolved in the slab, fine again during hot rolling As a result of the reprecipitation, the assembly became worse and the magnetism was weak. On the contrary, in the case of the invention material 5-8 satisfying the manufacturing conditions of the present invention, the magnetic properties were excellent.

As described above, the present invention has an effect of providing a non-oriented electrical steel sheet excellent in magnetic flux density and magnetic permeability is reduced by 30% or more after heat treatment, the demand compared to the time of shipment. In addition, according to the present invention, it is possible to secure excellent magnetic properties without undergoing hot rolling annealing and light rolling performed to ensure magnetic properties, thereby reducing the manufacturing process.

Claims (2)

In the manufacturing method of the non-oriented electrical steel sheet, By weight%, C: 0.02% or less, Si: 1.5% or less, Mn: 1.5% or less, P: 0.15% or less, S: 0.02% or less, Sol.Al: 0.005% or less, N: 0.007% or less, Sn: Slab composed of 0.03-0.3%, Ni: 0.05-0.7%, Cu: 0.03-0.5%, remaining Fe and other unavoidable impurities is reheated to 1100-1300 ° C, hot rolled and wound up to a temperature below 800 ° C. Pickling, followed by cold rolling at a reduction ratio of 70% or more, heating at a rate of 5 ° C / sec or more, annealing for 30 seconds-5 minutes in the temperature range of 600-800 ° C, and then processing 700 after demand processing Method for producing a non-oriented electrical steel sheet having excellent magnetic properties after heat treatment characterized in that it comprises a stress relief annealing in the temperature range of -850 ℃. In the manufacturing method of the non-oriented electrical steel sheet, By weight%, C: 0.02% or less, Si: 1.5% or less, Mn: 1.5% or less, P: 0.15% or less, S: 0.02% or less, Sol.Al: 0.05% or less, N: 0.007% or less, Sn: 0.03-0.3%, Ni: 0.05-0.7%, Cu: 0.03-0.5%, B: 0.0005-0.0050%, and re-heat the slab composed of the remaining Fe and other unavoidable impurities to 1100-1300 ℃ Winding at a temperature below 800 ° C, pickling, followed by cold rolling at a reduction rate of 70% or more, heating at a rate of 5 ° C / sec or more, annealing for 30 seconds-5 minutes in the temperature range of 600-800 ° C. Next, a method for producing a non-oriented electrical steel sheet having excellent magnetic properties after the heat treatment, characterized in that the demand is made, including the stress relief annealing in the temperature range of 700-850 ℃ after processing.